Floating materials such as oil, scum, foam and the like collect on the surface of water treatment basins and, if not removed, can adversely affect operation of the water treatment system. In some prior scum removal systems, for example as disclosed in U.S. Pat. Nos. 4,011,164; 4,014,795 and 4,166,036 a skimmer such as a blade or wiper is moved across a surface of the liquid to push or guide floating materials toward and into a scum receiver. Such scum removal apparatus must not only be quite large to cover a substantial surface of the basin, but also become quite complex when it is necessary to accommodate variable liquid levels in the treatment basin. In another type of prior scum removal apparatus, such as disclosed in U.S. Pat. Nos. 3,923,661; 4,024,063 and 4,154,678 a weir is positioned by a float or by other apparatus at the surface of the liquid in the treatment basin and a pump is mounted on the weir to draw liquid over the weir into a scum receiver, and to pump liquid and floating materials from the scum receiver to a processing arrangement installed on land. In such apparatus, the movement of floating scum into and over the weir is induced by the pump action and this not only limits the surface area from which the floating weir can effectively remove floatable materials, but also involves pumping a substantial amount of water from the treatment basin and thus reduces the overall efficiency of the water treatment system.